Phase Converter Circuit OCPD, Disconnect, Wire Sizing

[solace396]

The circuit is supplying a fixed piece of equipment to be wired 208 Delta with a 10.5 amp load, supplied by a 120/240 single phase panel.

The customer had already bought a 240 in 240 out rotary phase converter with 48 single phase FLA, and an autotransformer to buck the 240 to 208 before running through the phase converter, and it is rated for 3.68 kVA, 17.71 A, with a max breaker size of 20 A.

I already know that the autotransformer will need to be upsized to handle the phase converter inrush. After speaking with the manufacturer (RONK), they recommended that since the load is only 10.5 A to buy an autotransformer with at least a recommended 40 A breaker size to handle what the phase converter will be using from the line side.

I gathered that the line conductors to the phase converter and the ocpd are to be sized 125% of single phase fla on nameplate, which would be 60 A. According to code, should not that auto transformer be sized for me to put a 60 A breaker in the panel? And if somehow it is okay to put a 40 A OCPD, should my disconnect then be 40 A also because what's the point of a 60 A at that point?And also because 455.6(A)(2) is so confusing the way it's written, are my load side conductors coming out of the phase converter to be the same size as my line conductors? Or can I downsize them based on the load it's serving? Also 455.22 states that I will also need a magnetic motor starter, considering the load, can I put that on the load side of the phase converter with a 20 A overload?

Another side note, I want to tell the customer to take the equipment back and buy a 240 to 208 phase converter for simplicity but he's looking at a four month lead time and is trying to get this piece of equipment up and running ASAP. How can I potentially cut that lead time down?

Thank you for your time.

 

[ptonsparky]

What is the load? Motor?

 

[solace396]

Phase Converter Nameplate

KVA MAX: 10
VOLTS: 240/480
TYPE: 2P/4P
FLA 1∅: 48/24
LARGEST MOTOR: 5HP
MIN KVA: 1.5
BASE 3∅ AMPS: 22/11

Manufactured Leg Control Panel Nameplate

KVA: 10
VOLTS: 240
TYPE: 2P
PANEL AMPS: 22

 

[solace396]

Sorry the load is a coffee bean roaster (Joper Roaster BPR-15), heated by natural gas, I'll give the name plate rating of the equipment which doesn't give much.

ELECTRICAL INPUT: 208V 60HZ
FUSES: CLASS CC 30A
PHASES: 3 PH

And this is more info I found online

BURNER POWER: 41KW
POWER REQUIREMENTS: 18A
ROASTER FAN MOTOR: 1HP
COOLER FAN MOTOR: 1HP
DRUM GEARBOX: 0.5HP
COOLER GEARBOX: 0.25HP

The 10.5A I previously mentioned was what the customer told me not based on any information I have seen thus far.

 

[retirede]

You need to be sure the roaster isn’t expecting a 208 wye source. Many times, a machine will be expecting 120V to neutral for running controls, etc. If any of the motors are powered by a VFD, you’ll likely need a wye source.

 

[Little Bill]

No such thing as a 208V Delta.

 

[ptonsparky]

No such thing as a 208V Delta.

Why do I think if there is no neutral load, people assume it's Delta ?

 

[solace396]

I will double check to see if it is 208 wye, however there was no neutral on the leads. And apparently you can get 208 Delta from a phase converter and even autotransformers. And there will not be a vfd on the circuit.

 

[ptonsparky]

I will double check to see if it is 208 wye, however there was no neutral on the leads. And apparently you can get 208 Delta from a phase converter and even autotransformers. And there will not be a vfd on the circuit.

See post 6.

 

[solace396]

Not saying your wrong, I would just have to explained on how the open Delta configuration, figure d-d isn't Delta.

Regardless of that, what I am looking at are 3 phase leads with no neutral, how does a wye not have a neutral? I'm here to understand.

 

[jim dungar]

Not saying your wrong, I would just have to explained on how the open Delta configuration, figure d-d isn't Delta.

Regardless of that, what I am looking at are 3 phase leads with no neutral, how does a wye not have a neutral? I'm here to understand.

You are correct figure D-D is a 208V delta 'output', but that is not the diagram you are using if the transformer is before the phase convertor.

Why are you bucking the voltage before the phase convertor and not after?

How do you plan to deal with the grounding of the phase converter output? At least one leg will be common with the original 240V service and its grounding. It would be good to keep that leg identified.

 

[ptonsparky]

...
Regardless of that, what I am looking at are 3 phase leads with no neutral, how does a wye not have a neutral? I'm here to understand

The neutral is just not used.

A three phase wye connected motor does not use a neutral.

 

[solace396]

You are correct figure D-D is a 208V delta 'output', but that is not the diagram you are using if the transformer is before the phase convertor.

Why are you bucking the voltage before the phase convertor and not after?

How do you plan to deal with the grounding in the phase converter output? At least one leg will be common with the original 240V service and its grounding. It would be good to keep that leg identified.

Those are great questions. There's an 8x8 box I will install after the disconnect and between the face converter and the manufactured leg control panel. That is where I intend to bond the equipment ground from the panel across to the load side.

My original plan was to put that autotransformers after and wire it in that configuration. However the manufacturer was not confident of what that result would be considering the manufactured leg going through an auto transformer that already has a high variation of voltage. So I scrapped that and went with their recommendation to put it before and upsize it.

But now I'm thinking about telling him to take that auto transformer back and just get a three phase Delta or wye transformer depending on what the equipment actually is.

 

[solace396]

The neutral is just not used.

A three phase wye connected motor does not use a neutral.

Okay now that makes sense. However considering my previous comment. If the equipment is wye, I would need a (dry-type?) Transformer rather than an autotransformer. So out of that transformer, you're saying I would just need to bond that neutral to the enclosure, and just simply bring out an equipment ground?

 

[david]

where is the closes grounding electrode to where you would be placing the transformer

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[solace396]

As far as I can tell so far, I would need to place a grounding electrode myself. I will be pouring a pad in the basement for the phase converter, and building a rack with unistrut behind it that the disconnects and transformer and magnetic motor starter would go on. I would drill for an electrode through the basement floor.

 

[david]

if you drive a rod in the buildings basement that would not be bonding the transformer to the buildings existing grounding electrode or grounding electrode system, whatever applies to the building your working in

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[solace396]

Gotcha, yeah I will locate their existing ground point. But you're saying as a separately derived system, it doesn't necessarily need its own electrode tied to the existing system so long as it is tied in to the existing system.

 

[jim dungar]

Okay now that makes sense. However considering my previous comment. If the equipment is wye, I would need a (dry-type?) Transformer rather than an autotransformer. So out of that transformer, you're saying I would just need to bond that neutral to the enclosure, and just simply bring out an equipment ground?

If the equipment needs a wye, you will need a delta-wye transformer after your phase converter.

 

[solace396]

Now I still have the question concerning 455.6(A)(2). In sizing the conductors, I am basically assuming the line conductors are sized 125% of the single phase input FLA. However it makes no mention of line side or load side conductors, I would like to downsize my load side of the phase converter but is it saying that all of the conductors must be sized 125% of the input single phase FLA?